Summaries of newsworthy papers include Heart progenitors yield diverse cell types, Cells remember where they came from, Plant power, ‘Ethical’ stem cells under the spotlight, How cells get a LIF to pluripotency, A single-molecule optical transistor and A black hole not too big and not too small

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VOL.460 NO.7251 DATED 02 JULY 2009

This press release contains:

· Summaries of newsworthy papers:

Stem cells: Heart progenitors yield diverse cell types

Developmental biology: Cells remember where they came from

Geoscience: Plant power

Developmental biology: ‘Ethical’ stem cells under the spotlight

Stem cells: How cells get a LIF to pluripotency

Physics: A single-molecule optical transistor

And finally… A black hole not too big and not too small

· Mention of papers to be published at the same time with the same embargo

· Geographical listing of authors

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A newly identified set of human cardiovascular progenitor cells can give rise to the three major cell types found in the heart, a Nature paper reveals. The cells, which can be grown in culture, should boost our understanding of cardiovascular development and disease, and may prove useful in regenerative cardiovascular medicine.

The progenitors, isolated from human fetal hearts, can give rise to striated and smooth heart muscle cells, as well as endothelial ‘lining’ cells. Kenneth Chien and colleagues used two independent transgenic and gene-targeting approaches in human embryonic stem cell lines to show that purified populations of these cells can self-renew and expand before differentiation into more mature cell types.

[2] Developmental biology: Cells remember where they came from (pp 60-65; N&V)

Salamanders re-growing amputated limbs do so by producing tissue-specific progenitor cells. The find, reported in this week's Nature, challenges dogma and has important implications for our understanding of limb regeneration.

Previously it was thought that salamander limb amputation triggers remaining mature limb cells to generate ‘pluripotent’ stem cells that can produce the many missing types of tissue. But Elly Tanaka and colleagues now show that blastema cells do not become pluripotent during limb regeneration and instead retain a strong memory of their tissue of embryonic origin. Each tissue, they conclude, produces a different set of progenitor cells with restricted potential for restoring a part of the limb — so cartilage cells cannot make muscle and muscle cells cannot make cartilage. The findings have important implications for regenerative medicine and research into treatments that could restore adult body parts.

Terrestrial plants may have played a surprisingly vital role in maintaining carbon dioxide levels in the atmosphere over the past 24 million years, suggests a paper in Nature this week. It has seemed mysterious that, with environmental conditions that are thought to have been favourable for increased weathering rates, carbon dioxide levels did not fall below a certain minimum value.

Mark Pagani and colleagues simulated terrestrial and geochemical carbon cycles to investigate a negative feedback mechanism from plants that prevents further removal of carbon from the atmosphere. They find that vegetation activity in upland regions of active mountain ranges during this time period was severely limited; which in turn diminished biotic-driven silicate rock weathering. The suggested negative feedback mechanism could have stabilized minimum carbon dioxide concentrations during the past 24 million years.

The authors conclude that land plants may have had a role in maintaining minimum atmospheric carbon dioxide concentrations during the past 24 million years.

Most, if not all, cell types in the body can be reprogrammed to become stem-cell-like, suggests a review of the so-called ‘induced pluripotent stem (iPS) cells’ in this week’s Nature. But complete and uniform reprogramming needs to be achieved if the resulting iPS cells are ever to be used in the clinic.

Shinya Yamanaka was the first to reprogram mature, differentiated cells into iPS cells, by using a retrovirus to add in a handful of genes. The cells, which can differentiate into many other cell types, were hailed as an ethical alternative to mainstream stem cell production methods that involve destroying embryos and require hard-to-come-by human eggs. However, the process of reprogramming is inefficient and often incomplete.

In this review, Yamanaka considers the reasons for bottlenecks in iPS cell production and proposes a model in which most or all cells have the potential to become stem-cell-like, given the right conditions — the reprogramming genes must be expressed in a particular pattern, and some other non-genetic events, such as methylation levels, are probably crucial. It’s only when these factors can be reliably controlled that iPS cells are likely to achieve their full potential as key players in disease research, drug screening, toxicology and regenerative medicine.

A rare insight into how pluripotency is maintained in mouse embryonic stem (ES) cells is published in Nature this week. The research explains how the cytokine leukaemia inhibitory factor (LIF) communicates with cells in order for them to retain their proliferative potential.

LIF is used in mouse ES cell culture, and removing it pushes cells towards differentiation. LIF is not, however, required for pluripotency of human ES cells, which are more like LIF-independent pluripotent cells derived from the mouse epiblast. Hitoshi Niwa and colleagues show that two LIF signalling pathways are each communicating via different transcription factors. This means that there are parallel pathways that control pluripotency. This is the first work to describe the functional hierarchy of transcription factors that maintains self-renewal of mouse ES cells.

An optical transistor that uses photons to carry and manipulate information is revealed in this week’s Nature, bringing the prospect of quantum computers one step closer.

Vahid Sandoghdar and colleagues show that a single dye molecule can act as an optical transistor, weakening or amplifying a ‘source’ laser beam depending on the power of a second ‘gating’ beam.

The conventional electron-based transistor is one of the most influential inventions of modern times and is ubiquitous in present-day technologies. But photons have been mooted as a replacement for electrons because photons travel more quickly and in an unhindered fashion. The main hurdle to their use, controllability of nonlinear interactions at the nanometre scale, is overcome in this paper.

[7] And finally… A black hole not too big and not too small (pp 73-75)

The detection of an ultraluminous X-ray source is now the strongest observational evidence for the existence of intermediate-mass black holes, as reported in this week’s Nature.

Black holes vary in mass, with the supermassive types ranging from several million to several billion times the Sun’s mass, while the stellar-mass ones have masses several to several tens that of the Sun. Claims of the existence of intermediate-mass black holes, with masses from ~100 to 10,000 solar masses, have been controversial.

Sean Farrell and colleagues detected X-rays from the galaxy ESO 243-49 that exceed the upper limit of luminosity for normal stellar processes. Analysis of the X-ray data shows that the black hole outside the host galaxy’s centre has a lower mass limit that is 500 times the mass of the Sun.

[9] Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca Ridge (pp 89-93)

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***These papers will be published electronically on Nature's website on 01 July at 1800 London time / 1300 US Eastern time (which is also when the embargo lifts) as part of our AOP (ahead of print) programme. Although we have included them on this release to avoid multiple mailings they will not appear in print on 02 July, but at a later date. ***

[10] Helical extension of the neuronal SNARE complex into the membrane
DOI: 10.1038/nature08156

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